Department of Biological Sciences, Florida International University, Miami, FL, USA.
Acta Biotheor. 2020 Jun;68(2):271-274. doi: 10.1007/s10441-019-09361-z. Epub 2019 Aug 31.
The latitudinal gradient in species richness is perhaps the most fundamental pattern of biodiversity, yet a satisfactory explanation for its existence remains elusive. A geometric "mid-domain effect" is often cited as having potential to help explain the latitudinal gradient in species richness, but the logic underpinning this hypothesis is apparently built on two incorrect assumptions: (1) that a given great circle-usually the Equator-can constitute the geometric "mid-domain" of the Earth's surface, and (2) that geophysical or bioclimatic boundaries are of geometric relevance in the context of a global-scale mid-domain effect. This article gives a brief overview of the relevant literature and history of thought on the subject, and describes in clear and simple terms why a global-scale mid-domain effect cannot arise, and thus cannot possibly represent a mechanistic basis for the latitudinal gradient in species richness. Explicit acknowledgement of this fact is of great importance, as it allows us to dispense with a commonly cited hypothesis for the latitudinal gradient in species richness.
物种丰富度的纬度梯度可能是生物多样性最基本的模式，但对于其存在的满意解释仍然难以捉摸。通常认为，几何“中域效应”有可能有助于解释物种丰富度的纬度梯度，但支撑这一假设的逻辑显然建立在两个不正确的假设之上：（1）给定的大圆——通常是赤道——可以构成地球表面的几何“中域”，以及（2）在全球尺度的中域效应背景下，地球物理或生物气候边界具有几何相关性。本文简要概述了相关文献和思想史上关于这一主题的内容，并以清晰简洁的术语描述了为什么不可能出现全球尺度的中域效应，因此不可能成为物种丰富度纬度梯度的机制基础。明确承认这一事实非常重要，因为它使我们能够摒弃一个关于物种丰富度纬度梯度的常见假设。
